1. Field of the Invention
The present invention relates generally to emergency ejection seats used in aircraft.
2. Background of the Invention
Ejection seats are typically used in aircraft to provide rapid egress out of and away from the aircraft in the event of an emergency. Emergency ejection seat systems must protect the occupant during all phases of the ejection sequence. The seat must also accommodate the seat occupant during non-emergency operation of the aircraft. Finally, maintenance personnel should have easy access the various components of the seat to assure the operational readiness of the systems.
Emergency ejection seats generally follow a well defined sequence of operation. First, the aircrew member initiates ejection by pulling up ejection handles usually located alongside of or between the crewmember's legs. Once ejection is initiated, the crewmember is automatically restrained in the seat and a cartridge fires a gun catapult raising the ejection seat along fixed guide rails out of the aircraft. The canopy of the aircraft is either removed or shattered to allow for free exit from the aircraft. As the seat exits the aircraft, a rocket motor ignites producing thrust sufficient to propel the seat and its occupant away from the aircraft. The seat must also be propelled high enough to allow the main chute to deploy in the case of ejection at ground level. Pitot static tubes are used to determine the altitude and airspeed of the ejection seat. For ejection at low altitude and low airspeed, the crewmember is separated from the seat and the main chute deploys immediately following ejection. For ejection at higher altitudes and airspeeds a drogue chute is deployed as the seat leaves the aircraft rails to provide initial stabilization. Once the seat reaches the proper altitude and airspeed the crewmember is separated from the seat and the main chute deploys.
To minimize the chances of serious injury to the crewmember during ejection, the seat should be designed to absorb forces which otherwise would impact directly on the crewmember. In some prior art designs the ejection seat is constructed of heavy-weight material to add ballast to the system. In other prior art designs heavy survival equipment is stowed under the seat to provide the additional ballast. However, this extra weight (which otherwise may not be necessary) may affect the mission capabilities of the aircraft. Moreover, as aircraft are upgraded and new avionics or weapons systems must be accommodated, weight and storage space can become critical to proper functioning of the aircraft.
In addition to protecting the crewmember during an ejection sequence, the seat must provide safe, comfortable and efficient accommodation of the crewmember during normal flight activities. Ejection seats currently used in aircraft are adjustable only along the axis of the seat rails, which are typically angled slightly backward to provide a safe ejection trajectory. Thus, these seats can only be adjusted in one direction. Due to this limited capability, these seats cannot accommodate a wide range of aircrew member sizes. Even when the crew size is accommodated, the limited adjustment capability does not always provide optimal line of sight or comfort for the crewmember. In recent years the need to accommodate a greater range of crew sizes has increased dramatically with the increased number of female crewmembers.
Moreover, because emergency ejection seat systems are critical to aircrew safety the seat system must be regularly maintained. However, existing emergency ejection seats are constructed as a single integrated unit. Thus inspection and maintenance of even minor sub-components of the seat requires complete removal of the seat from the aircraft. Typically, the canopy of the aircraft must be removed prior to removing the ejection seat because of the size of the seat.